Method and apparatus for assigning radio resources and controlling transmission parameters on a random access channel

ABSTRACT

A method and apparatus for assigning radio resources and controlling parameters for transmission over a random access channel in wireless communications by enhancing a random access channel is disclosed.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. application Ser. No.11/924,493 filed on Oct. 25, 2007, which claims the benefit of U.S.Provisional Application No. 60/863,276 filed on Oct. 27, 2006, both ofwhich are incorporated herein by reference as if fully set forth.

FIELD OF INVENTION

The present invention is related to wireless communications.

BACKGROUND

In 3GPP UMTS (Third Generation Partnership Project Universal MobileTelecommunication System) wireless systems, the Random Access Channel(RACH) is an uplink (UL) transport channel that is used for transfer ofdata and/or control information in the absence of a dedicated radiolink. The RACH is mapped to the physical random access channel (PRACH).

Access to the RACH by a wireless transmit-receive unit (WTRU) is basedon a slotted-Aloha approach, with acquisition indication received from aradio access network (RAN). The WTRU must first acquire the channel bytransmitting a preamble, which comprises a signature sequence that israndomly selected among a set of predetermined sequences. The transmitpower of the initial preamble is determined by open loop power control,with parameters determined and broadcast by the RAN.

The WTRU then waits for an acquisition indication from a Node B, whichis signaled in the Downlink (DL) on the Acquisition Indicator Channel(AICH). When the Node B detects the PRACH preamble associated with RACHattempt, it echoes on the AICH an identical signature sequence toindicate to the WTRU to transmit over PRACH.

In the case where no AICH is detected, the WTRU increases itstransmission power by a predetermined amount and retransmits thepreamble in the next available transmission slot. The process isrepeated until the AICH is detected by the WTRU, or until a maximumnumber of preamble transmissions is reached. If a negativeacknowledgement is received or the maximum number of transmissions isreached, RACH access has failed and a backoff procedure is performed atthe medium access (MAC) layer.

In the case where a positive AICH is transmitted by the Node B, the WTRUtransmits the PRACH frame, which consists of a control part 10 and datapart 15 as shown in FIG. 1A.

The preamble and AICH procedure provide a way to for the WTRU to reservethe RACH as well as determine the right power for transmission. Thepower of the control part 10 is set with a fixed offset from the powerof the last transmitted preamble. The transmission power of the datapart 15 is set using a gain factor with respect to the control part,which is determined in the same way as other UL dedicated physicalchannels. The gain factor depends on the spreading factor that is usedfor the data part. Spreading factors 256, 128, 64 and 32 are allowed forthe PRACH data part.

Referring to FIG. 2, the AICH consists of a sequence of consecutiveaccess slots 20. Each access slot consists of two parts, anAcquisition-Indicator (AI) part 25 and a part 30 of duration 1024 chipswith no transmission. The part of the slot with no transmission 30 isreserved for possible future use. The spreading factor (SF) used forchannelization of the AICH is 256.

The transmission rate for RACH/PRACH is limited (single code withspreading factor 32) in existing 3GPP systems. One reason for thelimitation is to avoid excessive UL interference caused by WTRUs whentransmitting high rate bursts over RACH/PRACH. When a WTRU gains RACHaccess, it must independently select the transport format fortransmission. There is no way for the RAN to dynamically control thetransmission rate of WTRUs over RACH/PRACH.

SUMMARY

Disclosed is a method and apparatus for assigning radio resources andcontrolling parameters for transmission over a contention-based channelthat is used by a WTRU to transfer data and/or control information in anuplink to a radio access network (RAN). In one embodiment, a method andapparatus are disclosed for increasing the rate of data transmissionover the channel while limiting any resulting increase of noise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an existing frame format for a physical random accesschannel (PRACH).

FIG. 1B shows a frame format for a physical random access channel(PRACH) according to the present disclosure.

FIG. 2 shows a frame structure for an existing acquisition indicatorchannel (AICH).

FIG. 3 shows a structure for an AICH according to the presentdisclosure.

FIG. 4 is a functional block diagram of a portion of a representativewireless communication system with a WTRU and a Node-B.

FIG. 5 shows a method for distinguishing among different PRACH typesaccording to the present disclosure.

DETAILED DESCRIPTION

Hereafter, a wireless transmit/receive unit (WTRU) includes but is notlimited to a user equipment, mobile station, fixed or mobile subscriberunit, pager, or any other type of device capable of operating in awireless environment. When referred to hereafter, a base stationincludes but is not limited to a Node-B, site controller, access pointor any other type of interfacing device in a wireless environment.

Although described within the scope of 3GPP UMTS and UMTS TerrestrialRadio Access (UTRA) wireless communication systems, the followingembodiments and teachings are applicable to other wirelesscommunications technologies, including those systems employing randomaccess channels for uplink transmission.

FIG. 1B shows a proposed frame format for a physical random accesschannel (PRACH). FIG. 1B indicates several methods, not to be consideredexhaustive, which may be used individually or in any combination toincrease the transmission rate of PRACH frames. A first method includesdecreasing a spreading factor (SF) used on the data part 17. A secondmethod includes increasing the number of channelization codes used forthe data part 17. A third method includes increasing the order ofmodulations (e.g. using 8-PSK, 16-QAM, 64-QAM) and variable coding rates(i.e. MSC) for the data part 17. Optionally, the control part of thePRACH frame 12 may be modified to support the higher data rates. Anincrease in the transmission power of the control part is proposed toimprove the reliability of the pilot field when high data rates areused. Specifically, the power offset between the last preamble and thePRACH control part (Pp-m=P_(message-control)−P_(preamble)) may betransmission rate dependant, rather than having a single value.

Such an increase in achievable rates of RACH/PRACH may result in asignificant increase in the number of transport formats (i.e. slotformats) that need to be supported on the Data portion of the PRACH. Theslot format for the Control part 10 of the existing PRACH only providestwo bits in the transport format combination index (TFCI) field 35. Thiscurrently limits to four the number of transport formats that can besupported on the Data portion of the PRACH. To circumvent thislimitation, a new slot format is proposed for the control part 12 of thePRACH, shown in FIG. 1B. This new slot format may provide more than twobits in the TFCI field 37. For example, having 8 bits in the TFCI field35 would allow for up to 2⁸=256 different slot formats on the Dataportion 17 of the PRACH.

For backward compatibility this newly defined slot format, containingmore than two bits in the TFCI field 37, will need to coexist with theformer slot format which only provided for two bits in the TFCI field35. Having two different PRACH types coexist, the PRACH and anEnhanced-PRACH, brings a challenge for a base station to properly decodea PRACH since the base station currently has no means by which it canlearn which PRACH type a particular WTRU uses for the control part 10and data part 15 of its PRACH transmission.

This backward compatibility issue can be addressed by performing asegregation of the radio resources used by the PRACH in two groups. Onegroup is reserved for the PRACH transmissions using the old PRACH formatand another group is reserved for the Enhanced PRACH transmissions usingthe new PRACH format. This segregation can be ensured by the RAN throughdedicated radio resource channel (RRC) signaling or broadcast RRCsignaling. Three examples, not to be considered exhaustive or limiting,follow.

A first example, illustrated in FIG. 5, is segregation in the time slotsavailable for PRACH transmissions. The RAN could reserve a certainnumber of slots for PRACH transmission using a given PRACH format whilereserving another set of slots for PRACH transmission using anotherPRACH slot format. FIG. 5 illustrates one particular example ofsegmentation by access slot; other examples are possible.

A second example is segregation of the scrambling codes used for PRACHtransmissions. The RAN could reserve a certain number of scramblingcodes for PRACH transmission using a given PRACH format (e.g.traditional PRACH) while reserving another set of scrambling codes forPRACH transmission using another PRACH format (e.g. Enhanced PRACH). Theassignment of scrambling codes may be signaled by higher layers and byRRC broadcast signaling.

A third example is segregation of signature sequences used in the PRACHpreamble. The RAN could reserve a certain number of signature sequencesfor PRACH transmission using a given PRACH format (e.g. traditionalPRACH) while reserving another set of signature sequences for PRACHtransmission using another PRACH format (e.g. Enhanced PRACH). Anexample of how signature sequences can be segregated is shown in theTable 1, where P0 to P8 are reserved for PRACH and P9 to P15 arereserved for Enhanced PRACH. Note that this is just one realization ofsegregation by signature sequence; others are possible.

TABLE 1 PRACH Preamble Value of n Type signature 0 1 2 3 4 5 6 7 8 9 1011 12 13 14 15 PRACH P₀(n) 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 P₁(n) 1 −1 1−1 1 −1 1 −1 1 −1 1 −1 1 −1 1 −1 P₂(n) 1 1 −1 −1 1 1 −1 −1 1 1 −1 −1 1 1−1 −1 P₃(n) 1 −1 −1 1 1 −1 −1 1 1 −1 −1 1 1 −1 −1 1 P₄(n) 1 1 1 1 −1 −1−1 −1 1 1 1 1 −1 −1 −1 −1 P₅(n) 1 −1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 −1 1P₆(n) 1 1 −1 −1 −1 −1 1 1 1 1 −1 −1 −1 −1 1 1 P₇(n) 1 −1 −1 1 −1 1 1 −11 −1 −1 1 −1 1 1 −1 P₈(n) 1 1 1 1 1 1 1 1 −1 −1 −1 −1 −1 −1 −1 −1Enhanced P₉(n) 1 −1 1 −1 1 −1 1 −1 −1 1 −1 1 −1 1 −1 1 PRACH P₁₀(n) 1 1−1 −1 1 1 −1 −1 −1 −1 1 1 −1 −1 1 1 P₁₁(n) 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1−1 1 1 −1 P₁₂(n) 1 1 1 1 −1 −1 −1 −1 −1 −1 −1 −1 1 1 1 1 P₁₃(n) 1 −1 1−1 −1 1 −1 1 −1 1 −1 1 1 −1 1 −1 P₁₄(n) 1 1 −1 −1 −1 −1 1 1 −1 −1 1 1 11 −1 −1 P₁₅(n) 1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1

Increasing the data rate according to the disclosed method may increasethe amount of noise generated. In order to avoid excessive noise risecaused by high data rate RACH/PRACH bursts, the RAN may be configured tocontrol the interference generated by the WTRUs. Specifically, the RANmay indicate to the WTRU, prior to WTRU transmission of the PRACH frame,the maximum transmission rate and/or power that can be used fortransmitting the PRACH frame. Alternatively, a grant may bepre-configured (e.g. through RRC broadcast signaling) to allow the WTRUto start transmission and, optionally, the grant may be readjusted bythe UTRA Network (UTRAN) while the WTRU is transmitting over theEnhanced RACH.

The information signaled from the RAN to the WTRU may effectively limitthe system impact caused by the PRACH frame, while allowing the WTRU toselect the highest transport block size and maximize the efficiency ofthe RACH access. A grant-type signaling mechanism is disclosed, wherethe RAN indicates to the WTRU the maximum amount of UL resources thatcan be consumed for transmission of the PRACH frame. The followingnon-exhaustive list of example metrics and parameters is proposed, themetrics to be used individually or in any combination to determine whatUL resources should be granted for enhanced PRACH transmission.

A first example is maximum power ratio, which indicates the maximumpower ratio between the enhanced PRACH data part 17 and the control part12, or the maximum power ratio between the enhanced PRACH data part 17and the preamble power. The maximum power ratio is one possible measureof the transmission power of the WTRU. Controlling the power of the WTRUis one way of controlling noise rise or interference caused by the WTRUin the UL. This power control may be performed by the base station.

A second example of a metric for determining what UL resources should begranted for enhanced PRACH transmission is maximum transmission power,which indicates the maximum total power that the WTRU can use fortransmission of the PRACH frame with enhanced data part 17 and controlpart 12. The maximum total power can be determined as an absolute value(e.g. 20 dBm), or as a relative power with respect to the preamblepower. As with the previous example, controlling the power of the WTRUeffectively controls the noise rise or interference that is caused bythe WTRU in the UL. This power control may be performed by the basestation.

A third example of a metric is maximum RACH transport block size.Determination of this quantity allows the UTRAN to control interferencethat is generated by the WTRU by controlling the amount of time that theRACH is used.

A fourth example of a metric is transmission time interval (TTI) size.

A fifth example of a metric is a maximum amount of time (e.g. number ofTTI) the WTRU can transmit.

The value of the grant may be mapped to an index, where the mapping isknown by the WTRU and RAN. The mapping may be broadcast by the RAN overBCCH/BCH, configured through higher layer signaling or pre-configured inWTRU devices.

Various mechanisms are proposed in the following, to allow the RAN toconvey the information described above. These mechanisms can be usedindividually or in any combination.

In one embodiment, shown in FIG. 3, the control information is conveyedto the WTRU using an existing AICH or similar channel. Specifically, theRAN takes advantage of an acquisition indication that is sent betweenthe preamble and the PRACH frame to indicate to the WTRU the maximumtransmission rate. A proposed structure of an AICH is shown in FIG. 3.The first part 50 of the AICH access slot may have the same meaning asin the existing AICH, whereas the last part 40 which was previously thereserved part 30 contains the control information.

In one example embodiment, the number of chips in the above examples maybe retained: the first part, or AI part, 50 of the AICH may contain 4096chips and the second part 40 may contain 1024 chips. Using a SF256channelization code, a sequence of 8 real-valued signals can betransmitted over the 1024 chips. A predefined sequence of symbols, e.g.signature sequence, can be defined for each of the control informationlevels. The mapping between symbol sequence and control informationindex should be known at the RAN and the WTRU; this mapping may bebroadcast by the RAN, configured through higher layer signaling orpre-configured.

Alternatively, the last 1024 chips 40 of the AICH slot can beinterpreted as a new bit field (e.g. 4 bits) which contains the index ofthe control information, where channel coding may be used to increasedecoding reliability of the bit field.

Alternatively, the control grant may be conveying using any of: existingenhanced access gate channel (E-AGCH) and enhanced reverse gate channel(E-RGCH) to indicate “grant” for PRACH frames; the forward accesschannel (FACH) transport channel or similar channel; and the broadcastcontrol channel (BCCH) logical channel, which is mapped to the broadcastchannel (BCH) transport channel. In this case, the control informationis broadcast throughout the cell and may be either common to all WTRUsusing the PRACH, or signaled individually to WTRUs using RACH/PRACH. Inaddition one may use other new or existing physical layer signalingand/or L2 control channel to convey the control grant.

The RAN may make a decision as to the WTRU maximum transmission rateand/or power for each WTRU that has successfully acquired the RACHthrough the preamble mechanism. This decision may be made autonomouslyor be directed by the WTRU.

The RAN could make this decision independently for each WTRU that hassuccessfully acquired the channel. An example of a metric for this is alimit on the UL interference. Although effective when a single WTRU hasacquired the RACH channel, it may lead to inefficiencies when more thanone WTRU transmits on the RACH. In the latter case, a WTRU may beassigned a higher rate/power but may not need it. The extra assignmentto this WTRU would be lost, as no other WTRU could use it.

In this approach, the RAN tries to assign the capacity among the WTRUsbased on limiting UL interference, while at the same time maximizing theprobability that this extra capacity will be used. In order to achievethis, the RAN may require an indication as to the WTRU buffer occupancy.A higher occupancy would imply a higher probability of using the extracapacity. The WTRU need only provide a coarse indication of bufferoccupancy (e.g. low, medium, high, very high). This information could besignaled during the RACH preamble in several alternative ways. As oneexample, a trailer may be appended to the preamble message with thebuffer occupancy indication. Alternatively, the information may be codedin the preamble signature sequences; that is, reserving a set ofsignature sequences for each of the buffer occupancy levels.

FIG. 4 is a functional block diagram 300 of a portion of arepresentative wireless communication system with a WTRU 210 and aNode-B, or base station 220. The WTRU 210 and base station 220 are intwo-way communication with each other, and are both configured toperform a method such as one of the embodiments described above forincreasing a data transmission rate over a random access channel.

In addition to the components that may be found in a typical WTRU, theWTRU 210 includes a processor 215, a receiver 216, a transmitter 217,and an antenna 218. The processor 215 is configured to perform a methodsuch as one of the embodiments described above for increasing a datatransmission rate over a random access channel. The receiver 216 and thetransmitter 217 are in communication with the processor 215. The antenna218 is in communication with both the receiver 216 and the transmitter217 to facilitate the transmission and reception of wireless data.

In addition to the components that may be found in a typical Node-B, theNode-B 220 includes a processor 225, a receiver 226, a transmitter 227,and an antenna 228. The processor 225 is configured to perform a methodsuch as one of the embodiments described above for increasing a datatransmission rate over a random access channel. The receiver 226 and thetransmitter 227 are in communication with the processor 225. The antenna228 is in communication with both the receiver 226 and the transmitter227 to facilitate the transmission and reception of wireless data.

By way of example, embodiments may be implemented in a base station,wireless network controller, at the data link layer or the networklayer, in the form of software or hardware in a WCDMA FDD or long termevolution (LTE).

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmware tangiblyembodied in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) module.

What is claimed is:
 1. A method for a wireless transmit and receive unit(WTRU) to send data in enhanced uplink, the method comprising:receiving, at the WTRU via broadcast signaling, an indication associatedwith transmission, the indication comprising a maximum resourceallocation; and sending, at the WTRU, data in enhanced uplink inaccordance with the received maximum resource allocation.
 2. The methodof claim 1, wherein the maximum resource allocation indicates a maximumamount of transmission time.
 3. The method of claim 1, wherein data issent on enhanced random access channel (RACH).
 4. The method of claim 1,wherein data is sent on enhanced physical random access channel (PRACH).5. The method of claim 1, further comprising sending a plurality ofphysical random access channel (PRACH) slots, each PRACH slot comprisinga data part and a control part.
 6. The method of claim 5, furthercomprising varying a number of channelization codes used in the datapart.
 7. The method of claim 1, wherein the indication associated withtransmission further comprises at least one of: a maximum transmissionrate that can be used for transmitting a random access channel (RACH)frame; a maximum power that can be used for transmitting the RACH frame;a maximum ratio of a RACH data part power to a power of a preamble; anabsolute maximum total power for transmission of the RACH frame; amaximum power for transmission of the RACH frame relative to the powerof a preamble; a maximum RACH transport block size; or a transmissiontime interval (TTI) size.
 8. A wireless transmit and receive unit (WTRU)comprising: a processor configured for: receiving, via broadcastsignaling, an indication associated with transmission, the indicationcomprising an initial serving grant value; and sending in enhanceduplink in accordance with the received initial serving grant value. 9.The WTRU of claim 8, wherein the initial serving grant value comprisesan indication of a maximum ratio of data part power to control partpower.
 10. The WTRU of claim 8, wherein the processor is furtherconfigured for: receiving, via an enhanced absolute grant channel(E-AGCH), a second indication associated with transmission, the secondindication comprising a second initial serving grant value; and sendingin enhanced uplink in accordance with the second initial serving grantvalue.
 11. The WTRU of claim 8, wherein the processor is furtherconfigured for: receiving, via an enhanced relative grant channel(E-RGCH), a second indication associated with transmission, the secondindication comprising a second initial serving grant value; and sendingin enhanced uplink in accordance with the second initial serving grantvalue.
 12. The WTRU of claim 8, wherein the processor is furtherconfigured to send a plurality of physical random access channel (PRACH)slots, each PRACH slot comprising a data part and a control part. 13.The WTRU of claim 12, wherein the processor is further configured tosend data using more than one spreading factor for channelization codesused in the data part.
 14. The WTRU of claim 12, wherein the processoris further configured to vary a number of channelization codes used inthe data part.
 15. The WTRU of claim 12, wherein the processor isfurther configured to vary modulation in the data part.
 16. The WTRU ofclaim 12, wherein the processor is further configured to varytransmission power in at least one of the data part or the control part.17. A method for a wireless transmit and receive unit (WTRU) toestablish access to a channel using random access procedure, the methodcomprising: receiving an indication of a first set of availablesignatures for random access channel (RACH); receiving an indication ofa second set of available signatures for enhanced uplink transmission;randomly selecting, at the WTRU, a signature from the second set ofavailable signatures for establishing random access to enhanced uplink;and sending a preamble using the selected signature.
 18. The method ofclaim 17, further comprising: receiving an indication of a firstpreamble scrambling code reserved for random access channel (RACH); andreceiving an indication of a second scrambling code reserved forenhanced uplink, wherein the preamble is transmitted using the secondscrambling code when establishing access to enhanced uplink.
 19. Awireless transmit and receive unit (WTRU) comprising: a processorconfigured for: receiving an indication of a first set of availablesignatures for random access channel (RACH); receiving an indication ofa second set of available signatures for enhanced uplink transmission;randomly selecting a signature from the second set of availablesignatures for establishing random access to enhanced uplink; andsending a preamble using the selected signature.
 20. The WTRU of claim19, wherein the processor is further configured for: receiving anindication of a first preamble scrambling code reserved for randomaccess channel (RACH); and receiving an indication of a secondscrambling code reserved for enhanced uplink, wherein the preamble istransmitted using the second scrambling code when establishing access toenhanced uplink.